Apparatuses and methods for power regulation based on input power

ABSTRACT

Apparatuses and methods for power regulation based on input power using circuitry are disclosed herein. An example apparatus may include a reference circuit configured to receive a first voltage and a second voltage and to provide an output reference voltage at an output node having a value equal to the second voltage subtracted from the first voltage. The reference circuit may be configured to mirror a current of a first circuit coupled between the second voltage and a reference voltage through a second circuit coupled between the first voltage and the output node. The example apparatus may further include a power circuit configured to provide a third voltage based on the output reference voltage. The third voltage may have a value that is equal to the output reference voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/866,152, filed Sep. 25, 2015. This application is incorporated byreference herein in its entirety and for all purposes.

BACKGROUND

As electronic devices continue to evolve, there is a constant tensionbetween size, speed, and power consumption. In some cases, electronicdevices include internal logic circuitry that operates at a lowervoltage than externally coupled circuitry. However, when communicatingwith the externally coupled circuitry, internal components may berequired in the output circuitry working at the same or higher voltagethan the externally coupled circuitry. Such output circuitry componentsmay require more space and consume more power than the internalcircuitry, making it challenging to stay within power specifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus including an output buffer anda power regulator circuit according to an embodiment of the disclosure.

FIG. 2 is a block diagram of a power regulator circuit according to anembodiment of the disclosure.

FIG. 3 is a schematic diagram of a reference circuit according to anembodiment of the disclosure.

FIG. 4 is a schematic diagram of a power circuit according to anembodiment of the disclosure.

FIG. 5 is a block diagram of a memory according to an embodiment of thedisclosure.

DETAILED DESCRIPTION

Apparatuses and methods for power regulation based on input power aredisclosed herein. Certain details are set forth below to provide asufficient understanding of embodiments of the disclosure. However, itwill be clear to one having skill in the an that embodiments of thedisclosure may be practiced without these particular details. Moreover,the particular embodiments of the present disclosure described hereinare provided by a of example and should not be used to limit the scopeof the disclosure to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the disclosure.

FIG. 1 is a block diagram of an apparatus 100 (e.g., an integratedcircuit, a memory device, a memory system, an electronic device orsystem, a smart phone, a tablet, a computer, a server, etc.) including aoutput buffer 110 coupled to a power regulator circuit 120. The outputbuffer 110 may be configured to receive an input data signal DATA IN andto provide an output data signal DATA OUT from node 160. In someembodiments, the output butler 110 may be a cascode output buffer thatincludes p-type transistors 152 and 154 on the high side (e.g., coupledbetween the node 160 and a supply voltage, such as VDD), and n-typetransistors 156 and 158 on the low side (e.g., coupled between the node160 and a reference voltage, such as ground GND). The output buffer 110may further include a p-channel driver circuit 140 configured to providea voltage to the gate of the transistor 152 based on a value or the DATAIN signal, and include an inverter 142 configured to provide a voltageto the gate of the transistor 158 based on the DATA IN signal.

The power regulator circuit 120 may include a VX voltage regulator 122and a VDD-VX voltage regulator 124. The VX voltage regulator 122 >mayconfigured to be coupled to a supply voltage, such as (e.g., a firstvoltage) and may provide a stepped down voltage VX (e.g., a secondvoltage). The VX voltage may be a lower voltage used to drive circuitryof the apparatus 100. The VX voltage regulator 122 may be a directcurrent to direct current (DC/DC) voltage regulator, in someembodiments. The VX voltage may be provided to the gate of thetransistor 156 and to the inverter 142. The VDD-VX voltage regulator 124may receive the VDD voltage and the VX voltage, and may provide a VDD-VXvoltage (e.g., a third voltage) that is the difference between thesupply voltage VDD and the VX voltage. The VDD-VX voltage may beprovided to the e of the transistor 154 and to the low side of thep-channel driver circuit 140.

The apparatus 100 may include components configured to provide, inoperation, a DATA OUT signal to externally coupled circuitry thatoperates at a higher voltage differential (e.g., VDD voltage to areference voltage GND) than other components (e.g., operating betweenthe VX voltage and the GND voltage) of the apparatus 100, such astransistors 152, 154, 156, and 158 of the output buffer 110 or circuitryof the power regulator circuit 120. For example, the VX voltageregulator 122 may receive the VDD voltage, and may provide the VXvoltage. In some examples, the VDD voltage may be 3 volts and the VXvoltage may be 1.8 volts. the VDD-VX voltage regulator 124 may receivethe VDD voltage and the VX voltage and may provide the VDD-VX voltageusing current mirror circuits.

As previously described, in some embodiments the output buffer 110 maybe a cascode output buffer. The transistor 154 may be activated based onthe VDD-VX signal received at its gate and the transistor 156 may beactivated responsive to the VX signal received at its gate. In otherembodiments, the output buffer 110 may be a non-cascode buffer, and thetransistor 154 and the transistor 156 may be omitted, such that thetransistor 152 and the transistor 158 are each coupled directly to thenode 160. The p-channel driver circuit 140 may receive the DATA INsignal, the VDD voltage, and the VDD-VX voltage. The p-channel drivercircuit 140 may provide either the VDD voltage or the VDD-VX voltage tothe gate of the transistor 152 based on a value of the DATA IN signal.For example, if the DATA IN signal is a high logical value, thep-channel driver circuit 140 may provide the VDD signal to the gate ofthe transistor 152 to deactivate the transistor 152. Further, if theDATA IN signal is a low logical value, the p-channel driver circuit 140may provide the VDD-VX signal to the gate of the transistor 152 toactivate the transistor 152 to provide the VDD voltage to the node 160.

The inverter 142 may receive the DATA IN signal, the VX voltage, and theGND voltage. in enter 142 may provide either the VX voltage or the GNDvoltage to the gate of the transistor 158 based on a value of the DATAIN signal. For example, if the DATA IN signal is a high logical value,the inverter 142 may provide the GND signal (e.g., invert the logicalvalue) to the gate of the transistor 158 to deactivate the transistor158. Further, if the DATA IN signal is a low logical value, the inverter142 may provide the VX signal to the gate of the transistor 158 toactivate the transistor 158.

By using the VDD and VDD-VX voltages having a VX voltage differential todrive the high side of the output buffer 110, and by using the VX andGND voltages having a VX differential to drive the low side of theoutput buffer, the output buffer 110 may be implemented using similarcircuitry as other circuitry of the apparatus 100 that operate using theVX voltage. That is, none of the components of the output buffer 110 areever exposed to a voltage drop higher than VX. Further, by basing theoutput signal from the VDD-VX voltage regulator 124 on the VDD voltage,rather than driving to a fixed voltage based. on an assumed VDD voltage,the VDD-VX voltage may automatically follow changes to the VDD) voltage,which may improve reliability and robustness of the apparatus 100.Circuitry of the output buffer 110 and the power regulator circuit 120may meet standby power requirements assigned to the apparatus 100, andmay be capable of achieving switching speeds required of flash memory,such as at least 166 MHz. Such circuitry suited to operate using the VXvoltage may require smaller real estate, than circuitry operating at theexternal voltage, e.g. VDD, therefore reducing the overall apparatuscost. For example, the output buffer 110, and more generally theapparatus 100, may work correctly in an extended supply voltage range,possibly matching, non-overlapping supply voltage specification ranges,such as 1.8V+/−10% and 3.0V+/−10%.

FIG. 2 is a block diagram of a VDD-VX voltage regulator 200 according toan embodiment of the disclosure. The VDD-VX voltage regulator 200 may beimplemented in the VDD-VX voltage regulator 124 of FIG. 1. The VDD-VXvoltage regulator 200 may include a reference circuit 232 coupled to apower circuit 234. The reference circuit 232 may receive a VDD voltageand a VX voltage, and provide a VDD-VX_REF voltage. The power circuit234 may receive the VDD-VX_REF voltage and the VDD voltage, and providea VDD-VX voltage.

In operation, the reference circuit 232 may provide a VDD-VX REF voltagebased on the VDD and VX voltages. The reference circuit 232 may includecurrent mirror circuits and matching transistors to generate theVDD-VX_REF voltage. The power circuit 234 may provide the VDD-VX voltagebased on the VDD-VX_REF voltage and the VDD voltage. The power circuit234 may include a voltage amplifier, a voltage-to-current converter, anda current multiplier to increase responsiveness of the VDD-VX voltage tospikes in demand, which may be necessary when driving an output bufferat higher frequencies, such as 166 MHz or greater. In some examples, thepower circuit 234 may be disabled during a standby mode, and thereference circuit 232 may provide the VDD-VX_REF via a resistive line tohold the voltage at the VDD-VX node at a nominal value.

FIG. 3 is a schematic diagram of a reference circuit 300 according to anembodiment of the disclosure. The reference circuit 300 may beimplemented in the VDD-VX voltage regulator 124 of FIG. 1 and/or thereference circuit 232 of FIG. 2. The reference circuit 300 may include afirst circuit 310 that is matched with a second circuit 330. That is, avoltage drop across the first circuit 310 is approximately the same as avoltage drop across the second circuit 330. The reference circuit 300 isconfigured to generate a VDD-VX_REF voltage (e.g., output referencevoltage) that represents the same voltage drop from VDD as the voltagedrop from a VX voltage to a GND voltage. The first circuit 310 mayinclude p-type transistors 312 and 314, and the second circuit 330 mayinclude p-type transistors 332 and 334. The reference circuit 300 mayfurther include p-type transistors 316, 336, and 338; and n-typetransistors 318, 320, 322, and 342. The reference circuit 300 mayadditionally include capacitor 350 and capacitor 352.

A source of the transistor 312 may be coupled to a VX voltage source(e.g., the VX voltage regulator 122 of FIG. 1) and a drain of thetransistor 312 may be coupled to a source of the transistor 314. A drainof the transistor 314 may be coupled to the GND voltage. Thus, thevoltage drop across transistors 312 and 314 is the VX voltage. The drainof the transistor 312 is also coupled to the gate of the transistor 312and the gate of the transistor 316 to mirror the current through thetransistor 316 and the transistor 318. The drain of the transistor 314is also coupled to the gate of the transistor 314 to form a voltageclamp circuit.

A source of the transistor 316 may be coupled to the VX voltage sourceand a drain may be coupled to a drain of the transistor 318. A source ofthe transistor 318 may be coupled to the GND voltage. Thus, the voltage,drop across the transistors 316 and 318 is the VX voltage. Thetransistor 318 and the transistor 320 may form another mirror circuitwith both gates coupled together and to a drain of the transistor 320,such that the current through the transistor 320 is mirrored through thetransistor 318. The source of the transistor 320 may be coupled to theGND voltage.

A source of the transistor 332 may be coupled to the VDD voltage and adrain ma be coupled to a source of the transistor 334. A drain of thetransistor 334 may, be coupled to a node 340, which provides theVDD-VX_REF voltage. The voltage drop across the transistors 332 and 334of the second circuit is the VX voltage. A drain of the transistor 332is also coupled to a gate of the transistor 332 and a gate of thetransistor 336 to mirror the current through the transistor 336, thetransistor 338, and the transistor 320. The drain of the transistor 334is coupled to the gate of the transistor 334 to form a voltage clampcircuit.

A source of the transistor 336 may be coupled to the VDD voltage and thedrain may be coupled to a source of the transistor 338 to form a cascodedriver circuit. A drain of the transistor 338 may be coupled to a drainof the transistor 320, and a gate of the transistor 338 may be coupledto the node 340.

The transistor 342 and the transistor 322 may form a cascode drivercircuit. A drain of the transistor 342 may be coupled to the node 340,and a source may be coupled to a drain of the transistor 322. A sourceof the transistor 322 may be coupled to the GND voltage. A gate of thetransistor 342 may be coupled to the VX voltage source and a gate of thetransistor 322 may be coupled to a node between the transistor 316 andthe transistor 318 to provide feedback.

The capacitor 350 may be coupled in parallel with the second circuit 330between the VDD and the node 340 to form a tank circuit. The capacitor352 may be coupled between the node 340 and the node between thetransistor 316 and the transistor 318 to achieve a stable frequencyresponse.

In operation, the first circuit 310 and the second circuit 330 arematched such that a voltage drop across the first and second circuits310, 330 is the same liar a common current through each. Because thevoltage drop through the first circuit 310 is the VX voltage, mirroringthe current through the first circuit 310 to the second circuit 330 mayprovide a same voltage drop starting from a VDD voltage, such that thevoltage at the drain of the transistor 334 is VDD-VX. For example, thecurrent through the first circuit 310 is mirrored through the transistor316 and the current through second circuit 330 is mirrored via thetransistors 336, 338, and 320. The current through the transistor 320 ismirrored through the transistor 318. The transistor 322, which includesthe gate coupled to the node between the transistor 316 and thetransistor 318, throttles the current through the second circuit 330such that the currents through the transistor 316 matches the currentthrough the transistor 318. For example, if the current through thetransistor 316 is higher than the current through the transistor 318,the voltage at the gate of the 322 will be higher, and will cause morecurrent to be drawn through the transistor 322, and likewise through thesecond circuit 330. Conversely, if the current through the transistor316 is lower than the current through the transistor 318, the voltage atthe gate of the 322 will be lower, and will cause less current to bedrawn through the transistor 322, and likewise through the secondcircuit 330. Thus, the transistor 322 will throttle the current throughthe second circuit 330 such that the current through the transistor 316matches the current through the transistor 318, and likewise the currentthrough the first circuit 310 matches the current through the secondcircuit 330. By mirroring the current through the first circuit 310 andthe second circuit 330 and because of the common transistor sizes in thefirst circuit 310 and the second circuit 330, each of the first circuit310 and the second circuit 330 experience a similar VX voltage drop.Thus, the VDD-VX_REF voltage at the node 340 may be equal to a VDD-VXvoltage. The transistor 322 may provide feedback to improve reliabilityof the current mirroring, and the transistor 338 and the transistor 342may be included to form respective cascode driver circuits withtransistor 336 and transistor 322, respectively, for improved isolation.The capacitor 350 and the capacitor 352 may decrease noise in theVDD-VX_REF voltage provided at the output. Because the largest voltagedrop across any of the transistors 312, 314, 316, 318, 320, 322, 332,334, 336, 338, and 342 is the VX voltage, the same components may beused in the reference circuit 300.

FIG. 4 is a schematic diagram of a power circuit 400 according to anembodiment of the disclosure. The power circuit 400 may be implementedin the VDD-VX voltage regulator 124 of FIG. 1 and/or the power circuit234 of FIG. 2. The power circuit 400 may include a first circuit 410 anda second circuit 420 to form a voltage amplifier. The first circuit 410may include a transistor 412 and a transistor 414, and the secondcircuit 420 may include a transistor 422 and a transistor 424. The powercircuit 400 may further include p-type transistor 434, n-typetransistors 432, 436 and 438, a resistor 440, and a capacitor 452.

A source of the transistor 412 may be coupled to a VDD voltage and adrain of the transistor 412 may be coupled to a drain of the transistor414. A source of the transistor 414 may be coupled to a VDD-VX_REFvoltage (e.g., from the reference circuit 232 of FIG. 2 and/or thereference circuit 300 of FIG. 3). A gate of the transistor 412 may becoupled to the VDD-VX_REF voltage, and a gate of the transistor 414 maybe coupled to a drain of the transistor 414.

A source of the transistor 422 may be coupled to a VDD voltage and adrain of the transistor 422 may be coupled to a drain of the transistor424. A source of the transistor 424 may be coupled to a node 442. A gateof the transistor 422 may be coupled to the VDD-VX_REF voltage, and agate of the transistor 424 may be coupled to the drain of the transistor414. The transistor 422 and the transistor 424 may be larger replicas ofthe transistor 412 and the transistor 414 (e.g., have larger transistordimensions capable of providing greater current), respectively, to forma voltage amplifier. In some examples, the transistor 422 and thetransistor 424 may be four times larger than the transistor 412 and thetransistor 414, respectively.

A drain of the transistor 432 may be coupled to the VDD voltage and asource of the transistor 432 may be coupled to a source of thetransistor 434. Together, the transistor 432 and the transistor 434 mayact as a voltage to current converter. A drain of the transistor 434 maybe coupled to a drain of the transistor 438. The drain of the transistor438 may be coupled to the GND voltage. A gate of the transistor 432 maybe coupled to the drain of the transistor 424. A gate of the transistor434 may be coupled to the VDD-VX_REF voltage. A drain of the transistor436 may be coupled to the source of the transistor 424 and a source ofthe transistor 436 may be coupled to the GND voltage. A gate of thetransistor 436 may be coupled to a gate of the transistor 438. Thetransistor 436 may be larger than the transistor 438, to act as acurrent multiplier. For example, the transistor 436 may have largertransistor dimensions capable of providing greater current than thetransistor 438. The resistor 440 may be coupled between the node 442(e.g., a first output node) and the node 444 (e.g., a second outputnode) to isolate or decouple the second circuit 420 from the node 444providing the VDD-VX voltage. The capacitor 452 may be coupled betweenthe VDD voltage and the node 444 to filter out noise in the VDD-VXsignal.

In operation, the power circuit 400 provides the VDD-VX voltage at anoutput based on a comparison of transistor 412 and transistor 414 of thefirst circuit 410 with transistor 422 and transistor 424 of the secondcircuit 420. The transistor 422 and transistor 424 of the second circuit420, being larger, have a larger current capacity than the transistor412 and transistor 414 of the first circuit 410. Thus, the secondcircuit 420 may operate as a voltage amplifier, and the amplifiedvoltage may be based on a size different between the transistors 412 and414 of the first circuit 410 and the transistors 422 and 424 of thesecond circuit. Because the second circuit 420 may amplify a voltage,the transistor 432 and the transistor 434 (e.g., acting as a voltage tocurrent converter) and the transistor 436 and the transistor 438 (e.g.,acting as a current multiplier), may draw the amplified voltage down,e.g., reduce the voltage, such that the voltage at the source of thetransistor 424 (e.g., the node 442) is equal to the voltage at thesource of the transistor 414 (e.g., the VDD-VX_REF voltage). Because thesecond circuit 420 is coupled in parallel with the capacitor 452, thevoltages at the node 442 and the node 444 may each be equal to VDD-VX.The resistor 440 may isolate or decouple the node 442 (e.g., and thesecond circuit 420 from the node 444 to prevent coupling between theoutput and the second circuit 420.

FIG. 5 is a block diagram of a memory 500 according to an embodiment ofthe disclosure. The memory 500 includes an array 502 of memory cells,which may be, for example, DRAM memory cells, SRAM memory cells, flashmemory cells, or some other types of memory cells and may include anynumber of banks and/or sections of memory as described herein. Thememory 500 includes a command decoder 506 configured to receive memorycommands 508 through a CMD bus. The command decoder 506 may generatecontrol signals based on the memory commands 508 received through theCMD bus. The memory 500 may also include an address latch 510 configuredto receive address A0-AN signals 520 from an address bus. The addresslatch 510 may provide row and column addresses. The address latch thenoutputs separate column addresses and separate row addresses.

The row and column addresses are provided by the address latch 510 to arow address decoder 522 and a column address decoder 528, respectively.The column address decoder 528 selects columns of memory cells extendingthrough the array 502 corresponding to respective column addresses. Therow address decoder 522 is connected to word line driver 524 thatactivates respective rows of memory cells in the array 502 correspondingto received row addresses. The selected columns corresponding to areceived column address are coupled to a read/write circuitry 530 toprovide read data to a data output circuit 534 via an input-output databus 540.

The memory 500 may include circuit configured to operate at a lowervoltage than an operating voltage of an output bus to drive the outputdata. For example, an output bus may be specified to operate between aVDD voltage and a reference voltage. The circuitry may be designed tooperate between a VX voltage, which is less than the VDD voltage, andthe reference voltage, such as GND voltage. A power regulator circuit535 and the output buffer 534 may operate together to provide the outputdata using circuitry of the memory 500 by using the VDD-VX voltage alongwith the VDD, VX, and GND voltages. The power regulator circuit 533 mayinclude the power regulator circuit 120 of FIG. 1, the VDD-VX voltageregulator 200 of FIG. 2, the reference circuit 300 of FIG. 3, the powercircuit 400 of FIG. 4, or combinations thereof. Further, the outputbuffer 534 may include the output buffer 110 of FIG. 1. Write data areprovided to the memory array 502 through a data input circuit 544 andthe memory array read/write circuitry 530.

From the foregoing it will be appreciated that, although specificembodiments of the disclosure have been described herein for purposes orillustration, various modifications may be made without deviating fromthe spirit and scope of the disclosure. Accordingly, the disclosure isnot limited except as by the appended claims.

What is claimed is:
 1. An apparatus, comprising: a power regulatorcircuit configured to provide a second voltage based on the firstVoltage, wherein the power regulator circuit is further configured togenerate a third voltage based on the second voltage and the firstvoltage; and an output buffer configured to provide an output signalbased on an input signal, wherein a voltage of the output signal variesbetween the first voltage and a reference voltage, wherein a firsttransistor of the output buffer is configured to be driven using thefirst, voltage or the third voltage based on the input data and a secondtransistor of the output butler is configured to be driven using one ofthe second voltage or the reference voltage based on the input data. 2.The apparatus of claim 1, wherein the second voltage is less than thefirst voltage.
 3. The apparatus of claim 2, wherein each transistor ofthe power regulator circuit and each transistor of the output butler isconfigured to operate at a voltage differential that is equal to or lessthan the second voltage.
 4. The apparatus of claim 1, wherein the powerregulator circuit is configured to generate the third voltage based on adifference between the second voltage and, the first voltage. Theapparatus of claim 1, wherein the power regulator circuit is configuredto generate the third voltage, using current mirroring to subtract thesecond voltage from the first voltage.
 6. The apparatus of claim 1,wherein the power regulator circuit comprises: a first voltage regulatorconfigured to provide the second voltage based on the first voltage; anda second voltage regulator configured to provide the third voltage basedon the first voltage and the second voltage.
 7. The apparatus of claim6, wherein the first voltage regulator comprises a direct current todirect current voltage regulator.
 8. The apparatus of claim 7, whereinthe second voltage regulator comprises: a reference circuit configuredto provide an output reference voltage that is equal to the differenceof the first and second voltages; and a power circuit configured toprovide the t voltage based on the output reference voltage.
 9. Anapparatus, comprising: a reference circuit configured to receive a firstvoltage and a second voltage and to provide an output reference voltageat an output node, the output reference voltage having a value equal tothe second voltage subtracted from the first voltage; and a powercircuit coupled to the reference circuit and configured to provide athird voltage based on the output reference voltage.
 10. The apparatusof claim 9, wherein the reference circuit is configured to mirror acurrent of a first circuit configured to receive the second voltage andis reference voltage through a second circuit configured to receive thefirst voltage.
 11. The apparatus of claim 9, wherein the third voltagehas a value that is equal to the output reference voltage.
 12. Theapparatus of claim 9, wherein the power circuit comprises a voltageamplifier configured to amplify a voltage based on transistor sizedifference between the voltage amplifier and a third circuit and basedon the output reference voltage.
 13. The apparatus of claim 12, whereinthe power circuit comprises a current multiplier configured multiplycurrent flowing through the voltage amplifier to reduce the amplifiedvoltage from the voltage amplifier such that the third voltage isprovided to an output node.
 14. The apparatus of claim 13, wherein thepower circuit comprises a voltage-to-current converter configured toconvert the amplified voltage to current.
 15. The apparatus of claim 12,wherein a transistor of the voltage amplifier is larger than atransistor of the third circuit.
 16. The apparatus of claim 9, furthercomprising an output buffer configured to provide an output signal at anoutput node based on an input signal, wherein the output signal Variesfrom the first voltage to the reference voltage.
 17. The apparatus ofclaim 16, wherein the output buffer comprises a p-type transistorcoupled in series with an n-type transistor, wherein the output node isbetween the p-type transistor and the n-type transistor, a p-channeldriver configured to drive the p-type transistor using one of the firstvoltage or the third voltage based on the input signal; and an inverterconfigured to drive the n-type transistor using one of the secondvoltage or the reference voltage based on the input signal.
 18. Amethod, comprising: receiving a first voltage and a second voltage at avoltage regulator; mirroring a current of a first circuit of the voltageregulator through a second circuit of the voltage regulator; providing athird voltage based on the current through the second circuit of thevoltage regulator; and providing an output signal from an output bufferbased on an input signal using the first, second, and third voltages,wherein the output signal varies between the first voltage and areference voltage.
 19. The method of claim 18, wherein providing a thirdvoltage based on the current through the second circuit of the voltageregulator comprises subtracting the second voltage from the firstvoltage to provide the third voltage.
 20. The method of claim 18,providing the output signal from the output buffer comprises: providingone of the third voltage and the first voltage to a first transistor ofthe output buffer based on the input signal; and providing one of thesecond voltage and the reference voltage to a second transistor of theoutput buffer based on the input signal.